This penguin volume is the paperback and easily accessed translation of the 'Diary of Murasaki Shikibu', a fragmentary piece written by the author of the much more famous and inspired 'Tale of Genji'. As Genji is probably the best work in all the history of Japanese literature, and as we know so little about its author, this diary (which is a fragented remain of the possible original) has acquired a certain relevance it would otherwise lack from purely literary and quality arguments.
The diary as said is a fragmented and patched-up remain of the original one that Murasaki Shikibu might have noted down. It mainly describes the events of 2 years when she was in the service of Empress Shoshi at the Tsuchimikado Palace. The main event in more than half of the book is the birth of Prince Atsunada, son of Shoshi and the reigning Emperor (Go-Ichijo) and grandson of Fujiwara no Michinaga (the all-powerful regent of that period of Heian Japan). The first 50 or so sections describe in detail the ceremonies held and gives a glimpse of courtier life of the times, so different from the idealized view that Murasaki would forge in the Genji. Here the courtiers tend to be rude, unsubtle and drunk, and the ladies (Murasaki included) bored, insecure and with a high tendency to gossip and critizising everyone else. The second part of the book includes some semblances of fellow-maids and courtiers, some of which were famous poets on their own (Ise no Taifu, Akazome Emon, Sei Shonagon), some ritual Gosechi Dances at the Imperial Palace and Murasaki's absence from the Courtly World. As in all Heian-era diaries, the events described are interspersed with poems written by Murasaki and others for the occasion. Heian courtiers were expected to produce them quite spontaneously as a matter of fact.
Don't get me wrong: the diary as it is has its interest and its beauties. Some of the poems are very good, and some of the paragraphs have been clearly polished and noted down by a master writer, like the first scene of the book, describing the arrival of late autumn at the Tsuchimikado Palace and the lovely combination of the sight of the waters in the Palace lake with the sound of the chanting of the monks. Nevertheless, it is a work of marginal interest if you aren't extremely interested in Heian Japan, the court life of the eleventh century and/or Murasaki Shikibu. I consider it well worth the read, but definitely a minor, anecdotic text.
As for this edition: it is inspired in a previous one, made by Richard Bowring in the 80s and published by Princeton. The old text (it can still be bought second-hand) is more academic (which isn't necessarily a virtue for the lay reader) but has the advantage over the penguin edition in that it also includes the 'poetic memoirs' of Murasaki (that is to say, a colection of a bit over 100 poems by the author, most with explanatory prefaces). It is a pity that the Penguin edition discarted these poems, and being a very small volume, there would have been no space troubles about it.